Re: [PATCH v16 Kernel 5/7] vfio iommu: Update UNMAP_DMA ioctl to get dirty bitmap before unmap

[Kirti Wankhede <kwankhede@nvidia.com>]

On 3/25/2020 7:48 AM, Yan Zhao wrote:
> On Wed, Mar 25, 2020 at 03:32:37AM +0800, Kirti Wankhede wrote:
>> DMA mapped pages, including those pinned by mdev vendor drivers, might
>> get unpinned and unmapped while migration is active and device is still
>> running. For example, in pre-copy phase while guest driver could access
>> those pages, host device or vendor driver can dirty these mapped pages.
>> Such pages should be marked dirty so as to maintain memory consistency
>> for a user making use of dirty page tracking.
>>
>> To get bitmap during unmap, user should allocate memory for bitmap, set
>> size of allocated memory, set page size to be considered for bitmap and
>> set flag VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP.
>>
>> Signed-off-by: Kirti Wankhede <kwankhede@nvidia.com>
>> Reviewed-by: Neo Jia <cjia@nvidia.com>
>> ---
>>   drivers/vfio/vfio_iommu_type1.c | 54 ++++++++++++++++++++++++++++++++++++++---
>>   include/uapi/linux/vfio.h       | 10 ++++++++
>>   2 files changed, 60 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/vfio/vfio_iommu_type1.c b/drivers/vfio/vfio_iommu_type1.c
>> index 27ed069c5053..b98a8d79e13a 100644
>> --- a/drivers/vfio/vfio_iommu_type1.c
>> +++ b/drivers/vfio/vfio_iommu_type1.c
>> @@ -982,7 +982,8 @@ static int verify_bitmap_size(uint64_t npages, uint64_t bitmap_size)
>>   }
>>   
>>   static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>> -			     struct vfio_iommu_type1_dma_unmap *unmap)
>> +			     struct vfio_iommu_type1_dma_unmap *unmap,
>> +			     struct vfio_bitmap *bitmap)
>>   {
>>   	uint64_t mask;
>>   	struct vfio_dma *dma, *dma_last = NULL;
>> @@ -1033,6 +1034,10 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   	 * will be returned if these conditions are not met.  The v2 interface
>>   	 * will only return success and a size of zero if there were no
>>   	 * mappings within the range.
>> +	 *
>> +	 * When VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP flag is set, unmap request
>> +	 * must be for single mapping. Multiple mappings with this flag set is
>> +	 * not supported.
>>   	 */
>>   	if (iommu->v2) {
>>   		dma = vfio_find_dma(iommu, unmap->iova, 1);
>> @@ -1040,6 +1045,13 @@ static int vfio_dma_do_unmap(struct vfio_iommu *iommu,
>>   			ret = -EINVAL;
>>   			goto unlock;
>>   		}
>> +
>> +		if ((unmap->flags & VFIO_DMA_UNMAP_FLAG_GET_DIRTY_BITMAP) &&
>> +		    (dma->iova != unmap->iova || dma->size != unmap->size)) {
> potential NULL pointer!
> 
> And could you address the comments in v14?
> How to handle DSI unmaps in vIOMMU
> (https://lore.kernel.org/kvm/20200323011041.GB5456@joy-OptiPlex-7040/)
> 

Sorry, I drafted reply to it, but I missed to send, it remained in my drafts

 >
 > it happens in vIOMMU Domain level invalidation of IOTLB
 > (domain-selective invalidation, see vtd_iotlb_domain_invalidate() in 
qemu).
 > common in VTD lazy mode, and NOT just happening once at boot time.
 > rather than invalidate page by page, it batches the page invalidation.
 > so, when this invalidation takes place, even higher level page tables
 > have been invalid and therefore it has to invalidate a bigger 
combined range.
 > That's why we see IOVAs are mapped in 4k pages, but are unmapped in 2M
 > pages.
 >
 > I think those UNMAPs should also have GET_DIRTY_BIMTAP flag on, right?


vtd_iotlb_domain_invalidate()
   vtd_sync_shadow_page_table()
     vtd_sync_shadow_page_table_range(vtd_as, &ce, 0, UINT64_MAX)
       vtd_page_walk()
         vtd_page_walk_level() - walk over specific level for IOVA range
           vtd_page_walk_one()
             memory_region_notify_iommu()
             ...
               vfio_iommu_map_notify()

In the above trace, isn't page walk will take care of creating proper 
IOTLB entry which should be same as created during mapping for that 
IOTLB entry?


 >>>
 >>> Such unmap would callback vfio_iommu_map_notify() in QEMU. In
 >>> vfio_iommu_map_notify(), unmap is called on same range <iova,
 >>> iotlb->addr_mask + 1> which was used for map. Secondly unmap with 
bitmap
 >>> will be called only when device state has _SAVING flag set.
 >>
 > in this case, iotlb->addr_mask in unmap is 0x200000 -1.
 > different than 0x1000 -1 used for map.
 >> It might be helpful for Yan, and everyone else, to see the latest QEMU
 >> patch series.  Thanks,
 >>
 > yes, please. also curious of log_sync part for vIOMMU. given most 
IOVAs in
 > address space are unmapped and therefore no IOTLBs are able to be found.
 >
	
Qemu patches compatible with v16 version are at:
https://www.mail-archive.com/qemu-devel@nongnu.org/msg691806.html

Hope that helps.

Thanks,
Kirti